AC/DC’s Malcolm Young, whose death was announced Saturday at age 64, was not even the best known Young brother in the multimillion-record-selling rock band he founded. Angus Young, the lead guitarist in the school-boy outfit, got all the attention at the band’s sold-out concerts. But Malcolm was in many ways the band’s driving force, its most astute musician, a key songwriter and one of the best rhythm guitarists in the history of rock ’n’ roll.

AC/DC announced Malcolm Young’s death on its official Facebook page and website Saturday. The posts did not say when or where Young died. The guitarist was diagnosed with dementia in 2014, and was unable to accompany the band on its final tours, including Chicago stops in 2015 at Wrigley Field and 2016 at the United Center.

“It was Malcolm who had the vision of what the band should be,” Angus Young told the Tribune in 2003 as the band was about to be inducted into the Rock & Roll Hall of Fame. “He said, ‘We’re going to play the only music worth playing: rock ’n’ roll. And we’re going to play it hard.’”

The band went on to sell more than 200 million albums worldwide, though it was initially shunned by commercial radio and viewed as a pariah by some critics. But the band’s audience only expanded with each release. Its seventh studio album, “Back in Black,” (1980), is among the biggest sellers of all time, ranking in some estimations behind only Michael Jackson’s “Thriller.” And its sound became legendary — the band played elemental, no-nonsense riffs and terse, snarling, darkly humorous songs that bridged the gap between punk and metal and in many ways reduced rock ’n’ roll to its raw essence at a time when many mainstream rockers were going in the opposite direction.

A lot of that was Malcolm Young’s doing. He and Angus Young were the youngest of eight children born to a blue-collar family in Glasgow, Scotland. Their parents moved the family to Australia in 1963 to look for work. Within weeks of arriving in Sydney, their older brother, George, had formed a rock band, the Easybeats, which would storm the pop charts in 1967 with a classic garage-rock single, “Friday on My Mind.” Another one of their older brothers, John, introduced Angus and Malcolm to the blues, particularly Big Bill Broonzy.

“We would relate to what they were singing about,” Malcolm Young once told the Tribune of his childhood fascination with blues singers. “When a family uproots itself and moves to the other side of the world because your dad couldn’t get a job, you didn’t feel part of the system, if there even was a system. The blues singers were talking about everyday life, and they pushed a button in both of us.”

It was Malcolm who formed the band. He invited his younger brother, Angus, to join on guitar and then later found a singer, Bon Scott, already a veteran of the tough-as-nails Australian bar scene, a scene that AC/DC would soon captivate.

“Angus and I had silent dreams about playing in a band since we were kids, always playing our guitars and listening to records,” Malcolm Young once said in a Tribune interview. “I used to listen to the Beatles and Stones, whereas Angus was more into the heavier stuff — Cream, Hendrix — with the lead guitar. I would listen to songs as songs — the drums, the vocal, the music side of it. I tended to pick up on the chords, the whole picture around the guitar.”

To draw attention to the band, Malcolm and their sister advised Angus that his old schoolboy knickers and beanie would be a great way to gain attention from the hard-to-please bar crowd.

“The places we’d play were full of bikers, brawlers and drinkers coming off a day of work looking for a good time, and all these guys would be looking at me like Hannibal Lecter looking at his next victim,” Angus Young once told the Tribune. “We would come out and as soon as they saw me, they’d say, ‘What's this? Breakfast?’ Then we'd play, and the shock would hit: The fool can play! We played by feel. We felt as though you could put us on any stage, and we would find a way to win that crowd over. We had that attitude: We can't fail. You might not like it right now, but you will.”

Offstage, Malcolm and Angus both looked like street kids — they each stood barely 5 feet, 2 inches tall and weighed a little over 100 pounds. But with guitars in hand, they delivered knockout punches. In the recording studio, their riffs would dance in counterpoint, with Angus branching off to play leads while Malcolm kept the rhythm oil flowing with his unerring sense of time, his instinct for inserting a chord or riff at precisely the right moment.

“I was more into the chord thing, the complete song, rather than the solo part,” Malcolm Young once said. “I was more of a melodic player. Angus was more into the rock world. Straightaway, I said this is how we should do it. It was never a brotherly squabble, but the opposite, because we just wanted to do good as a band.”

In a separate interview with the Tribune in 2000, Angus Young elaborated on his brother’s often unsung but crucial role in the band: “In the beginning, we would sort of flip roles, then he took over on rhythm. His rhythm style is a style in itself. I sit and watch and try to copy him but it’s still not Malcolm. He’s got this amazing left hand, y’know? It’s just so quick, so fast … he’s always three or four moves ahead of us all. The adaptability of it — there’s all the chords I’ll struggle with, and he’s already hitting ’em. And on top of that, he keeps that right hand going, and it’s so smooth that there’s never a note missing. When you look at it, you go, ‘Aw, he’s just filling in spaces.’ But when you look at it closer, you realize he’s not only filling them in, he’s playing in between them. We sound like we do because of him.”

Their brother George Young and his Easybeats bandmate Harry Vanda produced the band’s early recordings, which grew from cult items into modest sellers thanks to the quintet’s relentless touring. Bon Scott’s clever, snarky, ribald lyrics — culled, he once said, from toilet-stall graffiti in Australian bars — were a perfect match for the Young brothers’ relentless riffs and brought the band to the precipice of fame.

The breakthrough finally came in 1979 with “Highway to Hell,” produced by South African producer Robert John “Mutt” Lange. It cracked the top 20 of the U.S. album chart and went on to sell more than 7 million copies, in part because Lange brought such ringing clarity and dynamic range to the band’s pummeling twin-guitar attack.

After mourning Scott’s death in 1980 (the singer was found dead in a car after a night of heavy drinking), Malcolm Young rallied the band. “Bon’s parents wanted us to go on, and after the funeral, Malcolm was the one who said the best way to get past this was to get back to work and write songs,” Angus Young said. The brothers recruited a singer that Scott admired, British rocker Brian Johnson, to handle lead vocals on what was to become the group’s landmark album, “Back in Black,” another Lange production.

Ever since, the band has been a steady presence in arenas and stadiums around the world, and put out a consistent stream of albums, never wavering from their ballad-free, harder-is-better approach. With the death of Scott, the recent retirement from live performances by Johnson due to hearing loss (he was replaced on recent tours by Guns N’ Roses’ Axl Rose), and now the death of Malcolm Young, the band’s future is once again murky.

But AC/DC’s legacy towers over the last 40 years of rock ’n’ roll, in large part due to the willpower, vision and working-class modesty of its founder.

“All we were doing is trying to entertain people,” Malcolm Young told the Tribune in 2003. “When we started as a band we were told by club owners that they wanted people to dance so they’d drink more. That’s how we cut our teeth — getting people hot and sweaty and drinking and enjoying themselves. We stayed on that and stayed true to it. People paid money for tickets to see us and be entertained by us, and we’ve never forgotten that. Anything after that was a bonus.”